Metastate annotations:

- return matches, "errors" reference
- NULL ==> not in a meta state



Things to do:

- check all files are closed

- fopen returns an open file
- fclose must be passed an open file
- fgetc, fputc must be passed an open file
- EOF return from fgetc; read error when EOF set
- fputc error return EOF
- ftell error -1L
- fseek error nonzero
- ferror - nonzero iff error indicator is set
- feof - nonzery iff eof is set


- + mode:
  input and output

  must call fseek between input and output, unless EOF!